Method and device for position detection

ABSTRACT

The present invention provides a method and device for position detection. For detection of a touch position, a segment of surface acoustic wave (SAW) is provided multiple times to be propagated on a SAW touch panel, and the multiple SAW segments are received by the SAW touch panel. In addition, during or after reception, partial output electrical signals are provided based on different portions of each received SAW segment to construct a complete output electrical signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/437,090, filed on Apr. 2, 2012.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and device for touch positiondetection, and more particularly, to a method and device for touchposition detection on large-size surface acoustic wave panel.

2. Description of the Prior Art

Surface acoustic wave (SAW) touch panel is a touch panel that determinesthe position of a touch input on a touch screen by sensing a SAW signalat a target location. It converts an electrical signal to the SAW signalby using a transducer including a piezoelectric material, and thendetermines whether the SAW signal is blocked and cannot be received whentraveling on the touch screen.

FIG. 1A is a schematic diagram illustrating the structure of aconventional SAW touch panel. As shown in FIG. 1A, a touch panel 10includes a screen area 11 and a reflection area 12. The reflection area12 includes a sensing device 13, which has a first and a secondhorizontal-axis transducer element 14 a and 14 b and a first and asecond vertical-axis transducer element 15 a and 15 b, wherein thesecond horizontal-axis and vertical axis transducer elements 14 b and 15b receive SAW signals Signal_V1 and Signal_V2 corresponding to inputelectrical signals Signal_Ei1 and Signal_Ei2 sent by the firsthorizontal-axis and vertical axis transducer elements 14 a and 15 a,respectively. In addition, the sensing device 13 further includes a setof first and second vertical-axis reflection units 16 a and 16 b and aset of first and second horizontal-axis reflection units 17 a and 17 b.These four reflection units 16 a, 16 b, 17 a and 17 b each includes aplurality of reflectors r. These reflectors r are all partiallytransmissive and partially reflective. Meanwhile, the SAW signalsSignal_V1 and Signal_V2 necessary for sensing a possible touch point Pinput on each horizontal axis and vertical axis are provided by thispartially transmissive and partially reflective effect of the reflectorsr. These reflectors r can be a wiring layer printed on a glass substrateof the touch screen, so cost of manufacturing is low. In addition, thereflectors r of the reflection units 16 a, 16 b, 17 a and 17 b are allarranged from sparse to dense (as seen from the traveling directions ofthe SAW signals Signal_V1 and Signal_V2). The reason for this is becausethat, in the case of evenly arranged reflection units 16 a, 16 b, 17 aand 17 b, the SAW signals Signal_V1 and Signal_V2 available forreflection for reflectors r at the back are less due to partialreflection. This affects the ability of the reflection units 16 a, 16 b,17 a and 17 b to accurately sense the positions of input touch pointscorresponding to the back parts thereof. Thus, the reflection units 16a, 16 b, 17 a and 17 b are arranged from sparse to dense to even the SAWsignal Signal_V1 or Signal_V2 input to each reflector r forcompensation. FIGS. 1B and 1C are diagrams illustrating electricpotentials of output electrical signals Signal_Eo1 and Signal Eo2 of theSAW touch panel shown in FIG. 1A without and with a touch point P input,respectively. In the diagrams, Vy represents the electrical potential ofthe output electrical signal Signal_Eo1, and is the X axis of thecoordinate of the input touch point P; Vx represents the electricalpotential of the output electrical signal Signal_Eo2, and is the Y axisof the coordinate of the input touch point P. The reason that theduration of Vx is longer than that of Vy is because the path traveled bythe second SAW signal Signal_V2 is longer. The depression shown in FIG.1C is a representation of the sensing of the touch point P, which is thebasis for determining the position of the touch point P input. Inaddition, at the beginning of Vy and Vx, there may be a spike (notshown) caused by the input electrical signals Signal_Ei1 and Signal_Ei2being received by the second horizontal-axis transducer element 14 b andthe second vertical-axis transducer element 15 b directly via the secondhorizontal-axis reflection unit 17 b and the second vertical-axisreflection unit 16 b immediately after input, respectively.

However, in large-size SAW touch panels, since the surface acoustic waveattenuates with the increase of the propagation distance and the numberof reflections traversed, as shown in FIG. 1E, the size of thedepression also reduces. Thus, it is possible that a touch further awayfrom the horizontal-axis and vertical-axis transducer elements 14 a and15 b is not detected because the size of the depression fails to exceeda threshold.

From the above it is clear that prior art still has shortcomings. Inorder to solve these problems, efforts have long been made in vain,while ordinary products and methods offering no appropriate structuresand methods. Thus, there is a need in the industry for a novel techniquethat solves these problems.

SUMMARY OF THE INVENTION

An objective of the present invention is to address the problem that aweak SAW signal on a large-size SAW touch panel due to long propagationdistance renders a touch too difficult to be distinguished. The presentinvention provides a segment of SAW multiple times to be propagated on aSAW touch panel, and provides partial output electrical signals based ondifferent portions of each SAW to construct a complete output electricalsignal. Each received SAW signal is amplified to different extends toovercome that the SAW signal becomes too weak due to long propagationdistance.

Moreover, the present invention further detects a position based on eachdepression in the complete output electrical signal.

The objectives of the present invention are accomplished by thefollowing technical scheme. A position detecting method proposed by thepresent invention, comprising: providing a SAW touch panel; providingmultiple SAW segments to be propagated on the SAW touch panel; receivingthe SAWs propagated on the SAW touch panel; and providing a segment ofpartial output electrical signal based on a different portion of eachreceived SAW and combining all of the partial output electrical signalsto form a complete output electrical signal.

The objectives of the present invention are further accomplished by thefollowing technical schemes.

A starting signal of a latter partial output electrical signal is largerthan that of an ending signal of a front partial output electricalsignal in the complete output electrical signal.

A wave number of a latter SAW segment is larger than a wave number of afront SAW segment in the multiple SAW segments.

Each segment of partial output electrical signal is generated based on again, the gain of a latter partial output electrical signal being largerthan the gain of a front partial output electrical signal.

Each segment of partial output electrical signal is within a predefinedrange.

The SAW touch panel is laid out with multiple segments of detectingareas, each segment of partial output electrical signal corresponding toa segment of detecting area.

The multiple detecting areas include multiple segments of detectingareas laid along a vertical axis of the SAW touch panel and multiplesegments of detecting areas laid along a horizontal axis of the SAWtouch panel.

Each segment of partial output electrical signal corresponds to a periodof time, wherein the period of time is in reference to a starting timefor receiving the segment of partial output electrical signal or astarting time for providing the segment of partial output electricalsignal.

The multiple SAW segments include multiple SAW segments initiallypropagated along a vertical axis of the SAW touch panel and multiple SAWsegments initially propagated along a horizontal axis of the SAW touchpanel, and the received SAWs include multiple SAW segments receivedalong the vertical axis of the SAW touch panel and multiple SAW segmentsreceived along the horizontal axis of the SAW touch panel.

The complete output electrical signal is in the form of saw-toothwaveform when the SAW touch panel is untouched.

The objectives of the present invention are accomplished by thefollowing technical scheme. A position detecting device proposed by thepresent invention, comprising: a surface acoustic wave (SAW) touch panelincluding a reflector array distributed on four sides of the SAW touchpanel and a sensing device, the sensing device including: a firstvertical-axis transducer element and a first horizontal-axis transducerelement for providing multiple SAW segments to be propagated on the SAWtouch panel; a second vertical-axis transducer element and a secondhorizontal-axis transducer element for receiving the SAWs propagated onthe SAW touch panel; and a control circuit for providing a segment ofpartial output electrical signal based on a different portion of eachreceived SAW and combining all of the partial output electrical signalsto form a complete output electrical signal.

A starting signal of a latter partial output electrical signal is largerthan that of an ending signal of a front partial output electricalsignal in the complete output electrical signal.

A wave number of a latter SAW segment is larger than a wave number of afront SAW segment in the multiple SAW segments.

Each segment of partial output electrical signal is generated based on again, the gain of a latter partial output electrical signal being largerthan the gain of a front partial output electrical signal.

Each segment of partial output electrical signal is within a predefinedrange.

The SAW touch panel is laid out with multiple segments of detectingareas, each segment of partial output electrical signal corresponding toa segment of detecting area.

The multiple detecting areas include multiple segments of detectingareas laid along the vertical axis of the SAW touch panel and multiplesegments of detecting areas laid along the horizontal axis of the SAWtouch panel.

Each segment of partial output electrical signal corresponds to a periodof time, wherein the period of time is in reference to a starting timefor receiving the segment of partial output electrical signal or astarting time for providing the segment of partial output electricalsignal.

The multiple SAW segments include multiple SAW segments initiallypropagated along the vertical axis of the SAW touch panel provided bythe first vertical-axis transducer element and multiple SAW segmentsinitially propagated along a horizontal axis of the SAW touch panelprovided by the first horizontal-axis transducer element, and thereceived SAWs include multiple SAW segments received along the verticalaxis of the SAW touch panel by the second vertical-axis transducerelement and multiple SAW segments received along the horizontal axis ofthe SAW touch panel by the second horizontal-axis transducer element.

The complete output electrical signal is in the form of saw-toothwaveform when the SAW touch panel is untouched.

With the above technical schemes, the present invention has atH leastthe following advantages and effects:

1. As to the amplification of the received SAW signals, wave number canbe increased to achieve this, and it is thus not limited to the gainperformance of hardware circuits; and

2. As to the different degrees of amplifications given to differentdetecting areas, the signals can be adaptively maintained in apredefined range, so that the size of an applicable SAW touch panel canbe significantly increased.

The above description is only an outline of the technical schemes of thepresent invention. Preferred embodiments of the present invention areprovided below in conjunction with the attached drawings to enable onewith ordinary skill in the art to better understand said and otherobjectives, features and advantages of the present invention and to makethe present invention accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thefollowing detailed description of the preferred embodiments, withreference made to the accompanying drawings, wherein:

FIG. 1A is a schematic diagram depicting a prior-art SAW touch panel;

FIG. 1B is a diagram illustrating the electrical potential of outputelectrical signals when the prior-art SAW touch panel has no touch;

FIG. 1C is a diagram illustrating the electrical potential of outputelectrical signals when the prior-art SAW touch panel has a touch;

FIG. 1D is a diagram illustrating the electrical potential of outputelectrical signals when a large-size SAW touch panel has a touch;

FIG. 2 is a flowchart illustrating a position detecting method accordingto a first embodiment of the present invention;

FIG. 3 is a schematic diagram illustrating signal extraction in thefirst embodiment of the present invention;

FIG. 4 is a flowchart illustrating a position detecting method accordingto a third embodiment of the present invention;

FIGS. 5A and 5B are schematic diagrams illustrating a touch positionthat spans over multiple segments of output electrical signals providedby a second embodiment of the present invention; and

FIG. 5C is a schematic diagram illustrating a touch position that spansover multiple segments of output electrical signals provided by a thirdembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Some embodiments of the present invention are described in detailsbelow. However, in addition to the descriptions given below, the presentinvention can be applicable to other embodiments, and the scope of thepresent invention is not limited by such, rather by the scope of theclaims. Moreover, for better understanding and clarity of thedescription, some components in the drawings may not necessary be drawnto scale, in which some may be exaggerated relative to others, andirrelevant parts are omitted.

As shown in FIGS. 1E and 1F before, signals are presented by the signalsreceived by the second horizontal-axis and vertical-axis transducerelements 14 b and 15 b after a string of continuous SAW is provided. Thesignals will gradually diminish, which affects the size of thedepression corresponding to a touch.

Referring now to FIG. 2, a position detecting method according to afirst embodiment of the present invention is shown. First, in step 210,each time a detection is made, multiple SAW segments are provided on aSAW touch panel. Then, in step 220, the multiple SAW segments arereceived by the SAW touch panel. The multiple SAW segments may includemultiple SAW segments initially propagated along the vertical axis ofthe SAW touch panel and multiple SAW segments initially propagated alongthe horizontal axis of the SAW touch panel. In addition, the receivedSAW segments may include multiple SAW segments received along thevertical axis of the SAW touch panel and multiple SAW segments receivedalong the horizontal axis of the SAW touch panel. Then, in step 230,during or upon reception, a partial output electrical signal is providedfor a different portion of each SAW segment, and a complete outputelectrical signal is constructed.

Referring again to FIG. 1, a position detecting device of the presentinvention includes a touch panel 10, which includes a screen area 11 anda reflection area 12. The reflection area 12 includes a sensing device13, which has a first and a second horizontal-axis transducer element 14a and 14 b and a first and a second vertical-axis transducer element 15a and 15 b, wherein the second horizontal-axis and vertical axistransducer elements 14 b and 15 b receive SAW signals Signal_V1 andSignal_V2 corresponding to input electrical signals Signal_Ei1 andSignal_Ei2 sent by the first horizontal-axis and vertical axistransducer elements 14 a and 15 a, and produce output electrical signalsSignal_Eo1 and Signal_Eo2, respectively. In addition, the sensing device13 further includes a set of first and second vertical-axis reflectionunits 16 a and 16 b and a set of first and second horizontal-axisreflection units 17 a and 17 b. These four reflection units 16 a, 16 b,17 a and 17 b each includes a plurality of reflectors r. Thesereflectors r are all partially transmissive and partially reflective.Meanwhile, the SAW signals Signal_V1 and Signal_V2 necessary for sensinga possible touch point P input on each horizontal axis and vertical axisare provided by this partially transmissive and partially reflectiveeffect of the reflectors r. These reflectors r can be a wiring layerprinted on a glass substrate of the touch screen, so cost ofmanufacturing is low. In addition, the reflectors r of the reflectionunits 16 a, 16 b, 17 a and 17 b are all arranged from sparse to dense(as seen from the traveling directions of the SAW signals Signal_V1 andSignal_V2).

The sending of the input electrical signals Signal_Ei1 and Signal_Ei2and the reception of the output electrical signals Signal_Eo1 andSignal_Eo2 are carried out by a control circuit (not shown). This is awell-known technique to those with ordinary skill in the art, thus itwill not further described. The control circuit performs the aboveposition detecting method. The control circuit may include, for example,a processor and a storage unit. The storage unit carries a program thatcauses the processor to execute the above steps 210 to 230.

Referring to FIG. 3, in an example of the present invention, multiplesegments of detection areas corresponding to the horizontal and verticalaxes are laid out on the SAW panel. Each segment of detection areacorrespondingly receives a different segment of the SAW. The abovemultiple SAW segments may include multiple SAW segments initiallypropagated along the vertical axis of the SAW touch panel and multipleSAW segments initially propagated along the horizontal axis of the SAWtouch panel. Take vertically propagated SAWs as an example, threedetecting areas P1, P2 and P3 are laid out in the vertical direction ofthe SAW panel, and three SAW segments are propagated. Corresponding tothese three SAW segments, SAWs W1, W2 and W3 are received, and outputelectrical signals Sw1, Sw2 and Sw3 are generated, wherein a partialoutput electrical signal S1 is generated based on a portion of thereceived SAW W1 corresponding to the detecting area P1; a partial outputelectrical signal S2 is generated based on a portion of the received SAWW2 corresponding to the detecting area P2; a partial output electricalsignal S3 is generated based on a portion of the received SAW W3corresponding to the detecting area P3, and these partial outputelectrical signals S1, S2 and S3 are combined to construct a completeoutput electrical signal Smix. Although the descriptions above are madein the context of the vertical axis, it is appreciated by one withordinary skill in the art that the above descriptions are equallyapplicable to the horizontal axis. In addition, the output electricalsignal Smix includes, but is not limited to, the partial outputelectrical signals S1, S2 and S3, as well as output electrical signalsbefore the detecting area P1 and output electrical signals after thedetecting area P3.

Although FIG. 3 shows three segments of partial output electricalsignals, it is appreciated by one with ordinary skill in the art thatthe above partial output electrical signals and the propagated SAWs canhave different number of segments, and the present invention is notlimited to this. Furthermore, the extraction of each segment of partialoutput electrical signal may be based on a time region corresponding todifferent detecting areas, wherein the time region may be in referenceto the initial time for receiving the SAW segment or the initial timefor providing the SAW segment, that is, a period of time since theinitial time for receiving the SAW segment or the initial time forproviding the SAW segment. The period of time for each SAW is notnecessarily the same.

In an example of the present invention, after the received SAWs W1, W2and W3 are converted into the output electrical signals Sw1, Sw2 andSw3, the partial output electrical signals S1, S2 and S3 are thenextracted from the output electrical signals Sw1, Sw2 and Sw3 toconstruct the complete output electrical signal Smix.

In another example of the present invention, during reception, theportions of the received SAWs W1, W2 and W3 corresponding to thedetecting areas P1, P2 and P3 are converted into the partial outputelectrical signals S1, S2 and S3, respectively.

Moreover, the present invention further includes amplifying the outputelectrical signal by increasing the wave number of the SAWs or raisingthe gain of converting the received SAWs to the output electricalsignals, so that the extracted partial output electrical signals S1, S2and S3 may be maintained in a predefined range.

In an example of the present invention, the output electrical signal israised by increasing the wave number of the SAWs. Each propagated SAWsegment can have a different wave number. For example, the wave numberof the third SAW segment is larger than that of the second SAW segment,and the wave number of the second SAW segment is larger than that of thefirst SAW segment. In other words, the wave number of at least one laterSAW segment is larger than that of at least one former SAW segment.Obviously, when the SAW touch panel is untouched, the above completeoutput electrical signal may be in the form of a partial or completesaw-tooth waveform. The region where the saw-tooth waveform is presentat least corresponds to a region in which the SAW panel is able todetect a touch, or corresponding to a region in which the abovehorizontal-axis and vertical-axis transducer elements or reflectors isable to reflect the SAWs to traverse the SAW touch panel.

In another example of the present invention, the output electricalsignal is raised by increasing the gain. A partial output electricalsignal can be extracted from each received SAW using a different gain.In other words, each output electrical signal is generated by thesensing device based on a gain; the gain of at least one later SAWsegment is larger than that of at least one former SAW segment, or thegain of at least one later partial output electrical signal is largerthan that of at least one former partial output electrical signal.

In yet another example of the present invention, the output electricalsignal is raised by increasing both wave number and the gain. Regardlessof which method is used to raise the output electrical signal, the sizeof a depression caused by a touch can also be increased.

According to the above, the output electrical signal can be maintainedin a predefined range when the SAW touch panel is untouched, and thesize of a depression caused by a touch can also be increased to adetectable level, such as greater than a threshold.

In a second embodiment of the present invention, a single SAW segmentcan be propagated, and the received SAW is then converted into multiplesegments of partial output electrical signals using multiple segments ofdifferent gains, and each segment of the partial output electricalsignals is maintained at a similar range. However, in large-size SAWtouch panel, the latter signals may attenuate to a range that is hard todetect, thus even if the gain is increased, it may still not be possibleto detect a touch and a touch position from the partial outputelectrical signal.

In a third embodiment of the present invention, when a depression spansover multiple adjacent segments of partial output electrical signals,another SAW segment is propagated, and a segment of output electricalsignal including the depression is generated based on the received SAWin order to accurately determine the touch position. For example, thecentroid position is calculated based on the depression.

In summary of the above, the present invention provides a positiondetecting method as shown in FIG. 4. In step 410, a complete outputelectrical signal is generated when a SAW touch panel is untouched. Thecomplete output electrical signal is formed by combining multiplesegments of partial output electrical signals generated based ondifferent parts of multiple SAWs. Then, in step 420, a complete outputelectrical signal is generated when the SAW touch panel is beingtouched. Thereafter, in step 430, this signal is compared with thecomplete output electrical signal generated at the time of no touch todetect any depression in the complete output electrical signal generatedat the time of touch, wherein the size of each depression is greaterthan a threshold. Then, in step 440, a position is detected based oneach depression. Furthermore, the above steps 410 to 440 can be carriedout by the control circuit.

Referring to FIG. 5A, a depression T1 corresponding to a touch spansover two partial output electrical signals S1 and S2 is shown. If thecentroid position is calculated based on this depression, since the sizeof depression is greater on the partial output electrical signal S2, sothe centroid position will skew towards the partial output electricalsignal S2. Thus, as shown in FIG. 5B, after determining that the size ofthe depression T1 is greater than the threshold, a SAW with acorresponding wave number corresponding to the range of the depressionT1 is propagated on the SAW touch panel, thus generating a partialoutput electrical signal Sr including a depression T2 that correspondsto the same touch. Since the output electrical signal is generated basedon the same SAW segment, so the determined centroid position moreaccurately represents the touch position.

In other words, the above steps 410 to 430 may be regarded as a firstdetecting stage, and upon detecting a depression spanning over multiplepartial output electrical signals, a second detecting stage is performedto detect the position represented by this depression spanning overmultiple partial output electrical signals.

The second detecting stage generates a second-stage SAW segment based oneach first-stage depression spanning over multiple partial outputelectrical signals, and generates a second-stage output electricalsignal based on the received SAW. The second-stage output electricalsignal is not in the form of saw-tooth waveform. Assuming thedepressions detected in step 430 are first-stage depressions, eachsecond-stage output electrical signal corresponds to a first-stagedepression spanning over multiple partial output electrical signals, anda second-stage depression is presented at a corresponding first-stagedepression. The above position is detected based on the second-stagedepression, that is, the above position is detected based on a portionof the second-stage output electrical signal that corresponds to theabove first-stage depression.

The wave number of the second-stage SAW can be generated based on thecorresponding first-stage depression spanning over multiple partialoutput electrical signals, for example, based on the wave number of theSAW corresponding to the first partial output electrical signal overwhich the first-stage depression spanned, or based on the wave number ofthe SAW corresponding to the last partial output electrical signal overwhich the first-stage depression spanned, or based on an average of theabove two.

The gain of the second-stage SAW can be generated based on thecorresponding first-stage depression spanning over multiple partialoutput electrical signals, for example, based on the gain correspondingto the first partial output electrical signal over which the first-stagedepression spanned, or based on the gain corresponding to the lastpartial output electrical signal over which the first-stage depressionspanned, or based on an average of the above two.

In a fourth embodiment of the present invention, when a depressionspanning over multiple partial output electrical signals correspondingto a touch is detected, then at least one of the latter or front partialoutput electrical signals in the depression range is adjusted (shrunk orenlarged), simulating a continuous detection waveform for detecting thetouch position. For example, as shown in FIG. 5C, based on the ratio rof the ending signal of the front partial output electrical signal tothe starting signal of the latter partial output electrical signal, thewhole latter partial output electrical signal is shrunk. In an exampleof the present invention, when the front partial output electricalsignal is already shrunken, the overall latter output electrical signalis shrunk by a ratio of the ending signal of the already shrunken frontpartial output electrical signal to the starting signal of the latterpartial output electrical signal. It can be appreciated by one withordinary skill in the art that the whole front output electrical signalcan be enlarged based on the ratio r of the starting signal of thelatter partial output electrical signal to the ending signal of thefront partial output electrical signal. Alternatively, the front andlatter output electrical signals can both be adjusted based on the ratior.

In other words, in the above step 440, at least one of partial outputelectrical signals corresponding to a depression spanning over thosepartial output electrical signals is enlarged or shrunk before positiondetection is performed.

For example, in the case that the starting signal of a latter partialoutput electrical signal is larger than the ending signal of the frontpartial output electrical signal in a complete output electrical signal,the partial output electrical signal to be enlarged is enlarged by aratio of a starting signal of a latter partial output electrical signalfollowing a partial output electrical signal corresponding to thepartial output electrical signal to be enlarged in the complete outputelectrical signal when the SAW is untouched to an ending signal of thepartial output electrical signal corresponding to the partial outputelectrical signal to be enlarged. Alternatively, the partial outputelectrical signal to be shrunk is shrunk by a ratio of an ending signalof a front partial output electrical signal preceding a partial outputelectrical signal corresponding to the partial output electrical signalto be shrunk in the complete output electrical signal when the SAW isuntouched to a starting signal of the partial output electrical signalcorresponding to the partial output electrical signal to be shrunk.

In the present invention, the touch position is determined based on thecentroid position as an example, but one with ordinary skill in the artcan appreciate that there are other methods of calculating the touchposition. However, these are not the focus of the present invention, andthus will not be further described herein.

Moreover, the detection of a depression can be made by comparing thecomplete output electrical signals at the time of no touch and at thetime of touch, or alternatively, by directly detecting on the completeoutput electrical signal at the time of touch; the present inventiondoes not put limit on this.

The above embodiments are only used to illustrate the principles of thepresent invention, and they should not be construed as to limit thepresent invention in any way. The above embodiments can be modified bythose with ordinary skill in the art without departing from the scope ofthe present invention as defined in the following appended claims.

What is claimed is:
 1. A position detecting method, comprising:providing a first surface acoustic wave (SAW) to a plurality ofreflectors of a SAW touch panel, wherein each pair of the plurality ofreflectors partially reflect the first SAW to output a first partiallyreflected SAW; receiving all of the first partially reflected SAWs toform a first output electrical signal; select a first portion of thefirst output electrical signal; providing a second surface acoustic waveto the plurality of reflectors, wherein each pair of the plurality ofreflectors partially reflect the second SAW to output a second partiallyreflected SAW; receiving all of the second partially reflected SAWs toform a second output electrical signal; select a second portion of thesecond output electrical signal; and forming a complete outputelectrical signal including the first portion of the first outputelectrical signal and the second portion of the second output electricalsignal.
 2. The method of claim 1, wherein a wave number of the secondportion is larger than a wave number of the first portion.
 3. The methodof claim 1, further comprising: providing a third surface acoustic waveto the plurality of reflectors, wherein each pair of the plurality ofreflectors partially reflect the second SAW to output a third partiallyreflected SAW; receiving all of the third partially reflected SAWs toform a third output electrical signal; select a third portion of thethird output electrical signal, wherein the complete output electricalsignal including further comprises the third portion, wherein the firstportion, the second portion and the third portion are within apredefined range.
 4. The method of claim 3, wherein the SAW touch panelis laid out with multiple segments of detecting areas, each of the firstportion, the second portion and the third portion corresponding to asegment of detecting area.
 5. The method of claim 4, wherein themultiple detecting areas include multiple segments of detecting areaslaid along a vertical axis of the SAW touch panel and multiple segmentsof detecting areas laid along a horizontal axis of the SAW touch panel.6. The method of claim 1, wherein the complete output electrical signalis in the form of saw-tooth waveform when the SAW touch panel isuntouched.
 7. A position detecting device, comprising: a surfaceacoustic wave (SAW) touch panel including a plurality of reflectors acontrol circuit for providing a first surface acoustic wave (SAW) to theplurality of reflectors, wherein each pair of the plurality ofreflectors partially reflect the first SAW to output a first partiallyreflected SAW; receiving all of the first partially reflected SAWs toform a first output electrical signal; select a first portion of thefirst output electrical signal; providing a second surface acoustic waveto the plurality of reflectors, wherein each pair of the plurality ofreflectors partially reflect the second SAW to output a second partiallyreflected SAW; receiving all of the second partially reflected SAWs toform a second output electrical signal; select a second portion of thesecond output electrical signal; and forming a complete outputelectrical signal including the first portion of the first outputelectrical signal and the second portion of the second output electricalsignal.
 8. The device of claim 7, wherein a wave number of the secondportion is larger than a wave number of the first portion.
 9. The deviceof claim 7, wherein the control circuit further performs the steps:providing a third surface acoustic wave to the plurality of reflectors,wherein each pair of the plurality of reflectors partially reflect thesecond SAW to output a third partially reflected SAW; receiving all ofthe third partially reflected SAWs to form a third output electricalsignal; select a third portion of the third output electrical signal,wherein the complete output electrical signal including furthercomprises the third portion, the first portion, the second portion andthe third portion are within a predefined range.
 10. The device of claim9, wherein the SAW touch panel is laid out with multiple segments ofdetecting areas, each of the first portion, the second portion and thethird portion corresponding to a segment of detecting area.
 11. Thedevice of claim 10, wherein the multiple detecting areas includemultiple segments of detecting areas laid along the vertical axis of theSAW touch panel and multiple segments of detecting areas laid along thehorizontal axis of the SAW touch panel.
 12. The device of claim 7,wherein the complete output electrical signal is in the form ofsaw-tooth waveform when the SAW touch panel is untouched.
 13. A controlcircuit, coupling to a sensing device of a surface acoustic wave (SAW)touch panel, which including a plurality of reflectors, performing thesteps: providing a first surface acoustic wave (SAW) to the plurality ofreflectors, wherein each pair of the plurality of reflectors partiallyreflect the first SAW to output a first partially reflected SAW;receiving all of the first partially reflected SAWs to form a firstoutput electrical signal; select a first portion of the first outputelectrical signal; providing a second surface acoustic wave to theplurality of reflectors, wherein each pair of the plurality ofreflectors partially reflect the second SAW to output a second partiallyreflected SAW; receiving all of the second partially reflected SAWs toform a second output electrical signal; select a second portion of thesecond output electrical signal; and forming a complete outputelectrical signal including the first portion of the first outputelectrical signal and the second portion of the second output electricalsignal.
 14. The control circuit of claim 13, wherein a wave number ofthe second portion is larger than a wave number of the first portion.15. The control circuit of claim 13, further performing: providing athird surface acoustic wave to the plurality of reflectors, wherein eachpair of the plurality of reflectors partially reflect the second SAW tooutput a third partially reflected SAW; receiving all of the thirdpartially reflected SAWs to form a third output electrical signal;select a third portion of the third output electrical signal, whereinthe complete output electrical signal including further comprises thethird portion, wherein the first portion, the second portion and thethird portion are within a predefined range.
 16. The control circuit ofclaim 15, wherein the SAW touch panel is laid out with multiple segmentsof detecting areas, each of the first portion, the second portion andthe third portion corresponding to a segment of detecting area, whereinthe multiple detecting areas include multiple segments of detectingareas laid along a vertical axis of the SAW touch panel and multiplesegments of detecting areas laid along a horizontal axis of the SAWtouch panel.
 17. The control circuit of claim 13, wherein the completeoutput electrical signal is in the form of saw-tooth waveform when theSAW touch panel is untouched.